Sunsets on Mars are blue because the dust in the Martian air is several times larger than the wavelength of visible light. Grains that size scatter light mostly forward, keeping blue in the tightest cone around the Sun while red and yellow spread across the sky, and their iron oxide absorbs much of the blue that strays. The result is a butterscotch day and, at sunset, when the light crosses far more dust, a cool blue glow around the Sun. Mars Rally Championship, a free browser rally game, paints a stylised version of it.
What a sunset on Mars actually looks like
The blue is local. A Martian sunset puts a pale blue to blue-grey glow around the Sun, an aureole in atmospheric-optics terms, brightest close to the disc and fading outward, while the rest of the sky stays yellow to orange. Turn your back on the Sun and the blue is gone.
The Sun itself sets smaller. Mars orbits about 1.5 times farther out than Earth, so the disc looks roughly two-thirds as wide and delivers less than half the light, yet it is still too wide for Phobos to black out. What Phobos and Deimos look like from the surface of Mars covers the transits Phobos makes instead, and the two moons that take over once the glow fades.
Why are sunsets on Mars blue? The dust is bigger than the light
A sky's colour depends on the size of whatever scatters the light, measured against its wavelength. Earth and Mars sit on opposite sides of that line.
On Earth the air does the scattering. Nitrogen and oxygen molecules, more than a thousand times smaller than visible wavelengths, sit in the Rayleigh scattering regime: blue at 450 nanometres scatters about six times as strongly as red at 700, forward and backward alike, so blue comes from every part of the sky. At sunset the direct beam crosses far more air, loses its blue, and arrives yellow, orange and red.
Mars has air too, about 95% carbon dioxide, but at about 6 millibars, under 1% of Earth's surface pressure, it is too thin to compete with the dust. The dust sets the colour, and the dust is big: Mars Pathfinder's sky images put the airborne grains at a mean radius of about 1.6 micrometres, some 3 micrometres across, four to eight times the wavelength of visible light.
Scattering by particles that size is called Mie scattering, and most of it goes forward. Much of that forward light is diffraction, bent around the grain's edge into a lobe whose width scales with wavelength over grain size. Treat a 3.2-micrometre grain as a tiny disc and the first dark ring of its diffraction pattern falls about 10 degrees from the Sun's direction for blue light at 450 nanometres, and about 14 degrees for red at 650. Real dust's spread of sizes blurs the rings, but the order holds: blue stays closest to the Sun.
The other half is chemistry. The dust is rust-coloured for the same reason the ground is: it is the finest fraction of Martian regolith, stained with iron oxide, which absorbs blue more readily than red. Light that passes through a grain and leaves at a wide angle comes out short of blue, so red and yellow fill the sky while blue stays in the forward lobe. Mark Lemmon of the Curiosity science team summed it up when NASA released the rover's 2015 sunset: "When the blue light scatters off the dust, it stays closer to the direction of the sun than light of other colors does."
Sunset brings it out. With the Sun low, its light crosses many times more dust than at midday, the disc dims, and the sky around it fills with forward-scattered light, bluest nearest the Sun. It is Earth's arrangement inverted: a warm sky with a cool sunset, instead of a cool sky with a warm one.
Mars vs Earth sunsets, side by side
Figures are rounded; Mars varies with season and dust.
| Earth | Mars | |
|---|---|---|
| What scatters most of the light | Nitrogen and oxygen molecules | Airborne iron-oxide dust |
| Scatterer size against 0.4–0.7 µm light | Over 1,000× smaller | About 3 µm across, 4–8× larger |
| Where the scattered light goes | Forward and backward about equally | Mostly forward, blue in the tightest cone |
| Colour spread across the whole sky | Blue, scattered about 6× as strongly as red | Red and yellow |
| Daytime sky | Blue | Butterscotch |
| Glow around the setting Sun | Yellow, orange, red | Blue to blue-grey |
| Surface pressure | ≈1,013 mbar | ≈6 mbar |
| Apparent width of the Sun | ≈0.5° | ≈0.35°, about two-thirds |
What color is the sky on Mars during the day?
Butterscotch, most days: a hazy yellow-brown. NASA's captions call it butterscotch in one image and red in another, and both are fair, because the shade moves with the dust aloft and with how a picture was processed.
The red is the dust's colour, not the air's, so the dust load sets the strength of the tint and of the sunset glow: under a clearer sky than usual, Perseverance's first sunset came out more muted than average. A big storm goes the other way, flattening the sky to a dark red-brown and then hiding the Sun, as the Mars dust storms explainer describes.
Real Martian sunset photos, 1976 to 2023
Viking 1 took the first, on 21 August 1976, about 15 minutes before sunset in Chryse Planitia; NASA keeps a gallery of Martian sunrises and sunsets taken since. The milestones:
- Mars Pathfinder, 1997 (sol 24): the red sky and the blue around the Sun, published as roughly what a human eye would see.
- Spirit, 19 May 2005 (sol 489): the Sun sinking behind the rim of Gusev crater, about 80 kilometres away.
- Curiosity, 15 April 2015 (sol 956): its first colour sunset, four frames over 6 minutes 51 seconds in Gale crater.
- InSight, 25 April 2019 (sol 145): shot from the camera on its robotic arm, released raw and colour-corrected.
- Perseverance, 9 November 2021 (sol 257): Mastcam-Z's first sunset, muted by a clearer sky.
- Curiosity, 2 February 2023 (sol 3,730): the first clear sun rays seen on Mars, shining through clouds at sunset.
Why Martian twilight lasts up to two hours
Martian twilight is long because the dust goes high. Pathfinder's twilight images, taken to map the dust's height, showed the sky staying bright for up to two hours after sunset, lit by dust still catching sunlight the ground had lost.
Twilight is also when Mars shows its clouds, mostly water ice no higher than about 60 kilometres. Curiosity has photographed night-shining clouds glowing after the ground goes dark, and the clouds behind its 2023 sun rays sat higher and colder than usual, possibly carbon dioxide ice.
The show repeats once a sol, about 40 minutes longer than an Earth day; how long a day on Mars lasts has the exact figure.
Is the blue sunset on Mars real?
Yes, and the evidence is more than one picture. Pathfinder, Spirit and Curiosity recorded blue around the setting Sun with different cameras at different landing sites, and the physics predicts it. What deserves suspicion is the exact shade in any single image.
Mars images come in three kinds, and JPL publishes the same scene in all three: raw, as the camera recorded it; natural colour, approximately what an eye on Mars would see; and white-balanced, lit as if by Earth light so geologists can read the rocks. White balance is the trap for skies. A Martian scene holds little blue, so the correction overcompensates: JPL notes that its white-balanced Mount Sharp panorama makes the sky look overly blue, where an eye would see butterscotch.
Every famous frame is processed. Spirit's 2005 filter set, by NASA's own caption, exaggerates the redness of the sky away from the Sun, and Curiosity's 2015 frames were white-balanced to remove camera artifacts. Pathfinder's sunset and InSight's colour-corrected one are the frames NASA presents as close to what an eye would see.
Blue has fooled people before. Viking 1's first colour picture, released in July 1976, showed a blue sky and was recalibrated to a reddish one within days. In February 2026 a viral blue Martian sunset turned out not to be a photograph at all: Snopes found Google's AI watermark, SynthID, in it, and a NASA spokesperson called it fan-made.
How Mars Rally Championship paints a Martian sunset
Mars Rally Championship does not simulate any of this scattering; it paints it. The game has four sun presets, SUNRISE, DAY, SUNSET and NIGHT, each a hand-picked palette of sky, horizon-dust and sunlight colours. Nothing in the sky shader knows a grain size or a wavelength.
SUNSET is the default: practice runs on both open stages, The Opener and The Long Run, are set at sunset. The daily challenge re-rolls the sky from the date, the same for every pilot, at 32% sunrise, 30% day, 26% night and 12% sunset, weighted away from the practice sky.
The palette is graded warmer than Mars: an ember red-orange horizon under a near-black maroon zenith, lit by a red-orange sun, closer to a dramatic Earth dusk than to a Mastcam frame. The blue is a fixed steel-blue halo on every daylight preset, the code's Mie halo, drawn as a ring about ten degrees out from the Sun with a warm corona inside it, where photographs show the blue brightest next to the disc. And the Sun never sets: the game keeps it above the horizon for the whole run, so there is no two-hour twilight.
One piece borrows the physics. The haze over distant ridges uses the sky's own colour function, so terrain fades into the sky behind it, and the haze thickens up to 2.2 times looking straight into the Sun: a one-line nod to forward scattering.
Where to race under a Martian sunset
- Stage 1 at sunset: The Opener under the sunset preset, steel-blue halo and all.
- Today's daily challenge: one seeded stage and sky for every pilot, sunset on about one day in eight.
- What it would actually be like to drive on Mars: the ground under that sky, at 3.72 m/s² of gravity.
- Mars Rally Championship is free, runs in a browser tab with no download and no account, works on a laptop, a phone in landscape or a school Chromebook, and races up to eight pilots live.